1. Field of the Invention
The invention relates to a photo-transistor in MOS thin-film technology, and somewhat more particularly to such photo-transistors, method of producing the same and a method of operating the same.
2. Prior Art
Photo-transistors are primarily bi-polar transistors with which the emitter-collector current is increased by photo-injection of minority carriers into the base. A present substantial disadvantage of such photo-transistors is an upper frequency limit at a few kilohertz.
A photo-transistor in MOS thin-film technology is described in G. Hass and R. E. Thun, Physics of Thin Films, Vol. 2, Academic Press (1964), in an article by P. K. Weimer, "The Insulated Gate Thin-Film Transistor", pages 147-192, at 187. The light-sensitive transistors described there consist of photo-conductive cadmium sulfide (CdS) and contains an insulation layer composed of silicon mono-oxide or calcium fluoride, which is additionally vapor-deposited onto the CdS layer. Deep and shallow volume traps below the conduction band are additionally filled by carriers produced by light (photons) and are then emptied by field ionization. As a result, the drain current increases due to a photo-current. This transistor is already conductive in the dark and exhibits poor transistor properties (distorted characteristics). Since the semiconductor body of this transistor is composed of a compound and the insulation layer must be additionally applied thereto, the manufacture thereof is difficult to reproduce.